The invention takes advantage of known properties of atmospheric pressure glow discharge. Atmospheric pressure glow discharge (APGD) has numerous applications due to operating at strongly non-equilibrium conditions in various gases, including air, at reasonably high power levels.
One particular form of APGD discharge is a dielectric barrier discharge (DBD), which is particularly interesting as it does not need sophisticated power supplies or circuitry.
Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier.
DBD plasma is typically obtained when the electrodes are separated by a gap of some millimeters and excited by alternating high voltage with frequency in the range 1 Hz-100 kHz. Typically in air, the DBD is formed by a large number of separate current filaments referred to as microdischarges. The microdischarges have a typical diameter in the range of 100 micrometers. These microdischarges have a complex dynamic structure and are formed by channel streamers that usually repeatedly strike at the same place as the polarity of the applied voltage changes, thus appearing as bright filaments.
In certain cases though, such as when the applied high voltage rise time is extremely short (for example dV/dt>1 kV/ns), the microfilaments may not form any stable pattern, and the discharge may appear uniform.
The persistence of streamers to strike at the same place of previous microstreamers is due to memory effect. The memory effect is associated with charge deposited on the dielectric barrier, as well as on residual charges and excited species in the microdischarge channel.
The DBD microstreamer pattern will generally have a regular pattern structure for any given material and a visible discharge may be observed as a result of the energy release from the plasma generated in the microstreamers.
The microstreamers are, however, extremely short lived—the avalanche to streamer transition generally takes about 10 ns, followed by the extinction of the microstreamers. The extinction voltage of the microdischarges is not far below the voltage of their ignition. Charge accumulation on the surface of the dielectric barrier reduces the electric field at the location of a microdischarge, which results in current termination within tens of nanoseconds after breakdown. The short duration of current in the microdischarges leads to low heat dissipation and, as such, the DBD plasma remains substantially non-thermal.
The characteristics of the DBD render the process suitable for many industrial applications such as ozone generation, medical applications, waste treatment, pollution control and surface treatment to promote wettability, printability and adhesion. Importantly, the DBD is non-destructive as there is no electrical arc generation between the electrodes.
As alternative to DBD, the dielectric barrier can be replaced by a highly resistive barrier. This may be accomplished by including one or more high value resistors in the circuit, or making the electrode of highly resistive material. This mode of operation is usually called RBD (resistive barrier discharge).